The millstones in use, each 52.5" (133 cm) in diameter, are surrounded by a wooden cover or 'tun', with the 'horse' supporting the 'hopper' and 'shoe'. When operated commercially, grain fell from a grain bin in the Garner, through a chute into the 'hopper', then slowly fed into the grain 'shoe'. This is agitated by the 'damsel', an iron rod located on the top of the 'rynd'. Grain shaken from the 'shoe' falls into the central 'eye' of the upper or 'runner' stone to be milled into wholemeal flour as it moves to the outer edge of the stones.
The middle picture shows the 'runner' stone being held on edge by the stone crane.  It enables stones, weighing up to a ton, to be lifted and inverted to clean or dress the stone. The 'runner' and the 'bed' stone are 'French' stones, each created from a number of pieces of hard flint-like stone, or burrs, that were quarried near Paris. Specialised stone masons would select a number of burrs before cutting them to produce the millstones, holding them together by circular iron bands and plaster of paris. The iron 'bar' or 'rynd' across the central 'eye' fits over the 'mace' on the stone spindle, balanced on the pivot point of the spindle, and turns the stone as the spindle rotates. Before being used, a new runner stone needs to be balanced to run smoothly by placing small lead weights into shallow holes in the top plaster surface. This runner stone is made from thirteen burrs with four inner and nine outer pieces. Many stones are made using more burrs, the open runner stone on the Stone Floor being made from 24 burrs.
The bottom picture shows the bed stone, fixed in position on the Stone Floor, and surrounded by the close-fitting wooden skirting. A hole in the skirting, but inside the surrounding 'tun', allows the meal produced by the millstones to fall down a chute to the Meal Bagging area on the floor below. The stone spindle protrudes through the center of the bed stone and is fitted with the thick cast-iron 'H' shaped 'mace', kept in position by the weight of the runner stone. The spindle emerges through the mace to form the pivot point upon which the 'rynd' and runner stone rest. This bed stone is made from four inner and eight outer burrs.